The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In the field of automatic transmissions, increasing the number of shift-stages is a useful technology for enhancement of fuel consumption and drivability of a vehicle. Increases in oil price have triggered competition in enhancing fuel consumption and efficiency of a vehicle.
Due to such competition, research has been undertaken to achieve weight reduction and to enhance fuel consumption by so-called downsizing. We have discovered that on an automatic transmission it is desirable to simultaneously provide better drivability and fuel consumption by achieving more shift stages.
In order to achieve more shift stages for an automatic transmission, the number of parts, especially the number of planetary gear sets, is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency.
Therefore, development of a planetary gear train capable of achieving improved efficiency with a reduced number of parts can improve fuel consumption by multiple shift-stages of an automatic transmission.
An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to six control elements (frictional elements), and may easily become long, thereby deteriorating installability.
In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements is sometimes attempted. However, such an arrangement may not be widely applicable, and using dog clutches may easily deteriorate shift-feel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.